On 25 August 2012, Voyager 1 said goodbye to our planetary system we know of as the Solar System and stepped out into interstellar space, the space between the stars. Voyager 2 is has either now followed or is in the process of doing so. It is a process to clarify where both these spacecraft are in relation to interstellar space.
The journey to the edge of the Solar System has been a long one.
Voyager 1 was launched on 5th September 1977. Think about that! That's a whole generation ago!
One interesting detail that is perhaps surprising to learn is that Voyager 2 was launched 16 days before Voyager 1, on the 20th August 1977. Voyager 1 however was faster and took the more direct route and so reached Jupiter first.
The mission was to explore the outer Solar System and the gas giants (though as an earlier blog recorded - these really should be renamed the liquid giants) their magnetospheres, atmospheres, structures, geology and 48 of their moons. Quite a mission for two spacecraft each the size of a small office about 4 metres by 4 metres by 4 metres, though there are various antennae attached too which are about 10 - 13 metres long. Each vehicle is considerably larger than the Pioneer spacecraft, yet they are nevertheless pretty small vehicles to navigate the then still relatively unchartered Asteroid Belt and beyond.
Volumes could be written on the incredible technology that is in each of these little crafts; technology that has been built on the success of the Pioneer spacecraft. For example, if Voyager 1 were to be above your head as you are reading your newspaper, it could read the headlines from one km away. Even more strange to think about is that we're talking about technology that is now around 38 years old! Think of how far even our computers have changed over that time and that gives us an idea of what NASA's Voyager teams are having to work with in still continuing to communicate with these spacecraft. Some of the computers that I used 35 years ago are now in a museum in Glasgow!
One of the first discoveries as mentioned in the previous blog is the unexpected shock to find that one of Jupiter's moons, Io, is actively volcanic and one such volcano is throwing sulpher and related material about 300km up which is roughly 30 times higher than Everest! When this comes down it covers an area of about the size of France! This of course has a lot to do with the fact that Io has a much weaker gravity than Earth so when it belches stuff out, it goes further. The fact that it is still active threw up as many questions as the volcanic material spewed out of Io's volcanoes.
The most memorable of the Voyager spacecraft moments though, was the pale blue dot photo. Voyager 1 turned around one last time to take a 'family photo' of all or as many of the planets in our Solar System as could fit into the camera view. On the 14th Feb 1990 it sent back (photo credit NASA) the following photo.
The Voyager Insterstellar Mission (VIM) is to explore the interstellar medium and the outer limits of the Sun's sphere of influence. VIM began when Voyager 1 was about 40 AU (40 times the Earth-Sun distance) and Voyager 2 was 31 AU from the Sun. They had both been travelling for 12 years.
The heliosphere, is what could be loosely described as the 'bubble' that the Solar System is in, which the solar wind creates. As the Sun and our whole Solar System moves through space, the front of the heliosphere is smaller than the rear. Voyager 1 was first to break through the heliosphere and the reason - or one of the reasons we know this is because of the
Sun's solar wind meeting the interstellar medium causing the solar wind to slow down dramatically because of what is known as the interstellar wind (illustrated in the following diagram - credit NASA). This shows the approximate positions of both spacecraft when Voyager 1 had just left the heliosphere in December 2004, then 94 AU from the Sun. Voyager 2 broke through the heliosphere on 30th August 2007 at 84 AU from the Sun which has shown us that in fact the heliosphere is not a perfect sphere but is dented, or at least has one dent we now know of. On the 25th August 2012, came the day when it is largely agreed Voyager 1 left the heliopause having travelled through the heliosheath to the interstellar medium, the space between the stars.
To have data sent back from interstellar space, is both stunning and remarkable. Both Voyager spacecraft will continue exploring and sending data back to Earth until possibly and hopefully around 2025 if nothing untoward happens to either of them along the way. Then, after their last signals 'home' they will continue to travel towards the stars, Voyager 1 passing the first one in about 40,000 years from now though passing at around 1.6 light years away from it, and Voyager 2 bound for the star Sirius, reaching it in about 296,000 years time (and that's even with the spacecraft travelling at around 40,000 mph!)
When, by 2025, the spacecraft will not have enough power left to operate any of its instruments or send signals back home, it will have been nearly 50 years since their launch! If they do continue to be in communication with Earth for this long, it will be with the children and grandchildren of the generation of those who engineered and steered its launch and first three year mission all those years ago. That's quite a thought isn't it!
Follow their progress with this http://voyager.jpl.nasa.gov/where/index.html link,
and on twitter using @NASAVoyager
